1. Field of the Invention
This invention relates generally to musical instruments, and more particularly to a musical instrument pad suitable for use in musical instruments.
2. Description of the Related Art
A pad is used for closing a tone hole on a woodwind musical instrument, including but not limited to a piccolo, flute, clarinet, saxophone, oboe, or bassoon. A pad contains a sealing surface, which is placed in contact with a corresponding tone hole when it is desired to close the tone hole. A pad is typically circularly symmetric about an axis normal to the sealing surface of the pad.
A pad is typically attached to a pad cup (a pad cup is also called “key cup” herein) of a musical instrument. The pad cup is typically situated at one end of a key mechanism. The key mechanism (“key” herein) may be actuated by a player of a musical instrument, and functions to open and close one or more tone holes located within the length of the musical instrument, which results in a change of pitch of the note being produced. The pad's position is usually fixed within the pad cup through the use of a pad adhesive, or by mechanical means involving any combination of screws, snaps, nuts, washers, and press-fit rings (also called grommets). When an adhesive is used to fix the pad in the pad cup, the process of positioning the pad, by heating the adhesive and adjusting the pad position relative to the pad cup, is known as “floating” the pad.
An effective pad has the following characteristics: a) it opens and closes a corresponding tone hole, typically as a result of light finger pressure or spring tension placed on the key; b) it produces as little noise as possible when contacting the tone hole; c) when in closed position, it makes a reliable and repeatable air-tight seal between the pad's sealing surface and the corresponding tone hole, preventing air (whose pressure is slightly higher than ambient air pressure) in the interior of the instrument (“bore” herein) from escaping through the tone hole.
When closing a tone hole, the position of the sealing surface of a pad relative to the tone hole is critical. In practice, any one or a combination of the following mechanical characteristics inherent in woodwind instrument key design may cause problems in sealing:                the pad cup moves in an arcuate motion about a center pivot point of the key, which is mounted on a small screw or small hinge rod;        the key is a complicated assembly of many parts brazed together that may have assembly tolerance positional errors, or may be in a bent or damaged condition. Positional errors may include translational error in three axes, and rotational error around two axes. (Because a pad is typically circular and symmetric about a centerline normal to the pad sealing surface, rotation about the vertical axis of a tone hole during installation does not affect pad effectiveness). Typically a pad is tolerant of some translational position error with respect to the tone hole, so long as the sealing surface of the pad remains level with the tone hole. By manipulating the pad orientation (known herein as “leveling”), through e.g., tipping of the pad within the pad cup, small errors may be corrected. When the pad has been positioned properly within its pad cup, it is said to be “leveled” with respect to the tone hole that it closes.        
For a pad to function properly, the pad must contact a tone hole with a light and uniform compression around a circle formed by the intersection of the top of the tone hole (“tone hole edge” herein) and a plane defined by an outer surface of the pad (known as “the sealing surface”), such that every portion of the tone hole edge is in contact with the pad. In order to produce an air-tight seal when a key is in the closed position, it is crucial that the sealing surface of the pad be at the proper height, and in the same plane as the tone hole edge. Adjusting a pad to effectively seal a tone hole is typically more difficult to achieve if the diameter of the pad cup is very nearly the same as the diameter of the tone hole (rather than the pad diameter being larger than the diameter of the tone hole) because there is a smaller tolerance for positional error.
If the key is in alignment with the tone hole, then it is typically easy to install and level a pad. In practice however, perfect alignment of key and tone hole is rarely the case, and labor necessary to achieve perfect pad alignment may be costly.
To cope with some alignment problems, several practices known in the art have developed. Adjustment of the pad's position may be accomplished by one or more of the following methods: selecting a thicker or thinner pad; floating the pad on a molten bed of pad adhesive (typically a hot melt glue) which is cooled to solidification after the part is in position; bending the key to change its position with respect to the tone hole; or adjusting the position of the pad through the use of thin paper shims placed between the back of the pad and the inside of the key cup. If heat sensitive pad adhesive is used for pad installation, once the pad is initially placed in the pad cup, a combination of light pressure and gentle warming can be used to adjust the pad so that the sealing surface of the pad conforms to the tone hole. A properly installed pad will have a small circular impression (pad seat) that is typically between 0.010 and 0.020 inches deep within the sealing surface of the pad. To create a pad seat, either a cushion layer or an outer sealing layer of the pad is slightly deformed. Seating is accomplished when every portion of the tone hole edge is in contact with the pad, and there is uniform contact pressure around the entire circumference of the pad seat.
It is crucial that pads be adjusted to be level, i.e., parallel to the plane of the corresponding tone hole edge prior to seating. A pad that is not leveled before seating will result in an unequal depth of impression, i.e., unequal compression around the circumference of the pad seat. Unequal compression of the pad materials does not remain stable over time. Due to elastic memory of the materials, regions of greater compression will tend to regain their original thickness, causing gaps between the pad seat and the edge of the tone hole over time, and consequent air leaks.
Prior art includes a non-beveled pad, a cross-section of which is shown in FIG. 1, and which may be assembled from straight-sided, die cut sheet materials (cork, silicone rubber, paper, cardboard, various polymer foams, and various pressure-sensitive adhesives) or from die cut laminated sheets of various combinations of sheet materials. A typical prior art non-beveled pad 10 as shown in FIG. 1 has a backer 120 (a backer is also called a backing layer herein) which is typically made of paper or cardboard, a cushion layer 140, a sealing layer 160, and a straight side wall 180 perpendicular to a plane defined by sealing surface 190. Typically, all layers, i.e., backer, cushion layer and sealing layer, are cut to a same diameter 122.
Problems with prior art non-beveled pads, such as that depicted in FIG. 1, may include difficulty controlling the final firmness of the pads, poor sealing characteristics of some materials, and heat sensitivity of some foam materials. Each of these problems may contribute to failure of the pad to seal properly after installation. Heat sensitivity (e.g., low melting temperature, propensity to deform upon heating) polymer foams is particularly problematic, often resulting in pad failure when a hot melt adhesive is used for installation.
FIG. 2 shows a cross-sectional view of a pad cup 210 and corresponding tone hole 220 prior to pad installation. A non-beveled pad is relatively easy to construct, but difficult to install correctly into a pad cup. Several problems can arise from the choice of a non-beveled pad. First, a non-beveled pad must fit entirely within pad cup inside diameter 230, and therefore the pad's diameter cannot exceed key cup inside diameter 230. Problems can arise if tone hole diameter 240 is approximately the same as pad cup inside diameter 230, because a non-beveled pad, e.g. pad 10 will typically meet tone hole edge 250 at the pad's outermost edge. As is known by those skilled in the art, a pad seat situated on the extreme outer edge of a pad makes a poor seal when attempting to close a tone hole. Second, as seen in FIG. 3, if a non-beveled pad 10 closely fits inside pad cup 210, pad side wall 180 tends to self-align with pad cup inside edge 340, which prevents making small adjustments, both in translation and rotation, of pad 10. Thus for a non-beveled pad, it is difficult to correct a misalignment of pad cup 210 with tone hole edge 250. Misalignment causes pad sealing surface 190 to be non-parallel to a plane defined by tone hole edge 250, resulting in air leakage when closing the tone hole 220 with pad 10.
Prior art also includes a traditional beveled pad 40, as shown in FIG. 4, made with multiple layers including: backer 420 containing one or more disks (typically made of cardboard) for stiffening; cushion layer 440 containing one or more disks typically made of wool felt, for cushioning an impact due to contact with a tone hole, and for reduction of noise; and membrane 460 typically made of bladder or leather, wrapped around the assembly and glued to backer 420, which membrane forms sealing surface 480 to make an air-tight seal with a tone hole. Traditional beveled pad 40 has its backer 420 cut to a smaller diameter 418 than diameter 422 of cushioning layer 440 that it supports. A beveled pad 40 having backer vertical side wall 424 and cushion layer side wall 448 is commonly called a “step-bevel” pad
Beveled pad 40 has two distinct advantages over non-beveled pad 20. First, as seen in FIG. 5 for pad 40 (membrane 460 has been omitted for clarity), cushion layer 440 has a diameter 422 that is larger than pad cup inner edge diameter 230, allowing cushion layer 440 to overhang pad cup inner edge 534, enabling better coverage of tone hole 220. Second, backer 420 has a backer diameter 418 that is smaller than pad cup inner edge diameter 230, resulting in some clearance between pad 40 and pad cup 210. The clearance allows for adjustment (e.g., via tipping) of pad 40 relative to tone hole 220, and may be accomplished by “floating” pad 40 on a bed of pad adhesive 550 that liquefies upon heating.
If a traditional step-beveled pad as depicted in FIG. 4 and FIG. 5, is sized to overhang pad cup 210, several drawbacks exist. The first drawback, as can be seen with reference to FIG. 2 and FIG. 5, is that thickness 546 of cushion layer 440 must precisely match projection distance 242 between plane 234 and plane 246. If cushion layer 440 is too thick or too thin, pad 40 will contact tone hole 220 unevenly, causing unequal compression of cushion layer 440, with eventual consequent air leaks. The second drawback, as seen in FIG. 4, is that cushion layer outer edge portion 442 is not supported by backer 420 because there is no direct contact with backer 420. Hence when the pad 40 contacts a tone hole 220, cushion layer outer edge portion 442 has the potential to flex when pressure is applied to pad 40 to close the tone hole 220, which flexing can result in a poor seal. Additionally, step-beveled pad 40 as shown in FIG. 5, relies upon contact with pad cup bottom edge 536 to support cushion layer outer edge portion 442. As will be recognized by one skilled in the art, any error in installation can result in cushion layer outer edge portion 442 unsupported by pad cup bottom edge 536, resulting in a higher likelihood of air leakage when tone hole 220 is closed by pad 40.